Conventional computer displays, such as cathode my tube (CRT) displays, liquid crystal displays, electroluminescent displays, and the like present a light output representing characteristics of an image. The image may be a graphical or pictorial one, an artistic one without any particular form, an alphanumeric one (including various alphabets and/or number systems), etc. Usually the image is presented on a screen which may be flat or somewhat curved, it being appreciated that substantial effort currently is being expended in providing developments for improvements in flat displays, such as those known as flat panel displays.
Usually such conventional displays must be sufficiently large to permit the displayed image, whether graphical, alphanumeric, or other, to be viewed comfortably by a person. Exemplary displays used on portable computers usually have a diagonal dimension exceeding nine inches. Some personal organizer type computers, such as those known as a personal digital assistant, have smaller displays, but in any event the display must be sufficiently large to be read by a person. Usually the larger the display, the greater the cost. Also, the larger the display, the greater the weight.
Displays also are used in automatic bank teller machines and the like, public telephones, and for televisions in public places, such as on an airplane. It would be desirable to provide privacy for such displays and possibly also for other displays.
For example, imagine an automated teller machine of the kind found at a bank. While using the machine, personal/confidential information may appear on the display. It is highly desirable that this information not be visible to other people in the area. Consider a public telephone of the type that contains a display. There may be occasions when the user would prefer that the information on the display not be visible to others.
Some airplanes have a flat panel display located at each seat. Passengers that pay a fee can see a video. The airlines may find it desirable that those who do not pay be unable to see the display. From another standpoint, it is desirable that people who do not choose to see the video not be annoyed by their neighbors who have chosen to watch the video.
Over the years substantial effort has been applied to expand the viewing angle for many displays. For example, off-axis viewing can be enhanced in a liquid crystal display by using optical retarders, as is disclosed in U.S. Pat. No. 4,385,806. However, a disadvantage when a display has a wide field of view is the lack of privacy; for example, as an individual is working on a portable computer while riding on a public vehicle, another rider may too easily observe the display. Another disadvantage is the wide distribution of light output that may occur when there is a wide angle of view provided by a display; such wide distribution may reduce the brightness, intensity and/or contrast of the display.
An effort is made herein to distinguish between field of view and angle of view (also referred to sometimes as viewing angle). A field of vie usually refers to how wide an image looks or appears to the eye or how much of a display is able to be seen at one time. The angle of view is usually refers to the angle at which one looks at or can look at an image, display, etc. For example, a narrow angle of view at which a monitor (or some other display device) must be viewed means that although the full monitor can be viewed, such viewing can be had from only a relatively small spot, or even from one spot or position. However, that monitor may present a relatively wide field of view to the viewer. As another example, in a heads up speedometer display of an automobile, the angle of view usually is relatively narrow so only the driver sees the display,; but the field of view usually is sufficiently wide to permit all of the desired information to be seen by the driver.
One prior approach to provide privacy in viewing a display has been to use a head mounted display which is supported on the head of a user (or on some other body part, for example), a helmet mounted display, etc. and provides a closed area in which the eye(s) view(s) the images provided by the display. Such displays sometimes provide increased immersion into the image whereby the user can observe the displayed images without being distracted by other visual stimuli, etc. Another technique for increasing the private viewing of a display has been to use a binocular, telescope or microscope type system through which the observer looks to see an image.
It is desirable that a display have adequate comfort with which images can be viewed and adequate eye relief. One aspect of comfort is the distance at which the image is viewed or appears to be located relative to the viewer's eye(s); a comfortable viewing distance is about 20 inches or more, for example, approximate reading distance. This distance physically can be changed using lenses, e.g., eyeglasses, but the apparent distance of the image should be maintained at a comfortable distance of, for example, 20 inches or more. An aspect of eye relief is the distance between the eye and the last optical element closest to the eye, such as the output objective of a microscope, telescope, etc. Often, it is desirable that such distance be relatively large to provide adequate eye relief. Without adequate eye relief and/or comfortable viewing distance, a person's eye(s) may be strained to view an image and/or otherwise caused discomfort.
In a helmet mounted display (sometimes referred to as a head mounted display), lenses may be placed at the eyes of the viewer (person) to reduce the physical size of the display system. The viewing angle and the field of view usually are relatively wide, which helps to accomplish immersion in the image. Eye relief may be relatively small because the user's (viewer's) face usually is mounted next to the viewing system. The head box is relatively small; this is acceptable because the head position is known and fixed with respect to the "sweet spot". The head box is the volume in which the viewer's head or face may be placed to see an image produced by a display. Often the head box is bounded by width, depth and height dimensions. Usually, anywhere a viewer puts the head relative to or in a head box, the intended image can be seen. In a head mounted or helmet mounted display the head box usually is limited to the area of the display and the head is located in a relatively fixed position to the optical components, and the head box is relatively small; in the present invention as is described below, preferably the head box is a location or position remote from the optical components of the viewing system and may be relatively large. The sweet spot is the position, location or point in space, generally over an extended area, at which the eyes must be positioned relative to the optical components of the display or viewing system so as to see (view) the image as well as possible. Sometimes the image may be seen when the eyes are at other than the sweet spot, e.g., near the sweet spot but not precisely there, but usually the best appearance of the image is when viewed from the sweet spot.
In contrast to a helmet mounted display, in a private viewing system it would be desirable to have the following characteristics. Lenses would not be needed to view the image because the image can be viewed relatively from afar. A narrow viewing angle would be acceptable to enhance privacy. Eye relief would be relatively large, for example, being as much as several feet, such as when the display being viewed is one for showing a video on an airplane, a bank teller machine, a telephone, etc. Additionally, the head box would be relatively large with a relatively large sweet spot that allows the display to be seen with one or possibly with both eyes and affords the possibility of back-and-forth (in-and-out), up-and-down, and side-to-side head movement relative to the display image source and sweet spot, for example.
A problem with many prior display systems is the relatively large amount of power required to operate the display. For example, a power hungry display is especially disadvantageous in a battery powered computer, in a video display used in a vehicle, such as an automobile, aircraft, watercraft, etc., where there may be a limited supply of power. It also would be desirable to reduce the power required for a display and/or the power requirements of a device, such as a computer, video display system, etc., which uses a display.
Removal or reduction of glare in or on a display is another problem for which substantial effort has been expended in the past. Glare usually is due to the reflection of ambient light from a display screen, monitor, liquid crystal display, cathode ray tube, electroluminescent display, etc. Most efforts in the past to try to reduce glare also have reduced the brightness of the image presented by the display. It would be desirable to reduce glare while minimizing the impact on the brightness of the image presented by a display.
With the foregoing in mind, then, there is a need to provide private viewing of an image from a source.